For injecting fuel into combustion chambers of an internal combustion engine, in particular a diesel engine, injection systems are used which in recent years have been increasingly implemented as so-called common rail systems. In these systems, the injectors disposed in the combustion chambers are supplied with fuel from a shared accumulator or common rail, the fuel to be injected being present in the accumulator at a pressure of up to 2000 bar.
Increasingly exacting requirements are being placed on the accuracy of the injection pressure of such injection systems for internal combustion engines which is required for injecting fuel into the engine's combustion chambers. Corresponding pressure control methods are therefore becoming increasingly important.
DE 10 2006 018 164 B3 discloses a method for pressure control of a common rail injection system of the type referred to in the introduction. With this known method, the volume flow of fuel into the high-pressure pump is adjusted using a volume control valve upstream of the high-pressure pump. Pressure control is performed via a pressure control valve disposed downstream of the high-pressure pump. Only one control mode is possible, i.e. either a volume control valve (VCV) closed-loop control mode or a pressure control valve (PCV) closed-loop control mode.
If pressure control is carried out via a volume control valve (VCV) closed-loop control mode as a function of the respective operating point, large overshoots must always be taken into account in transient phases, e.g. on the overrun or in the event of negative setpoint gradients, because the volume control valve or more precisely the high-pressure pump is very sluggish. This is obviously detrimental to the pressure control response.